The present invention is related to wireless communication systems, and in particular to channel selection in wireless communication systems.
In many industrial settings, control systems are used to monitor and control inventories, processes, and the like. Often, such control systems have a centralized control room with a host computer that communicates with field devices that are separated or geographically removed from the control room.
Generally, each field device includes a transducer, which may generate an output signal based on a physical input or generate a physical output based on an input signal. Types of transducers used in field devices include various analytical equipment, pressure sensors, thermistors, thermocouples, strain gauges, flow sensors, positioners, actuators, solenoids, indicators, and the like. Traditionally, analog field devices have been connected to the process subsystem and the control room by two-wire twisted-pair current loops, with each device connected to the control room by a single two-wire twisted pair loop. Typically, a voltage differential is maintained between the two wires of approximately 20 to 25 volts, and a current between 4 and 20 milliamps (mA) runs through the loop. An analog field device transmits a signal to the control room by modulating the current running through the current loop to a current proportional to the sensed process variable. An analog field device that performs an action under the control of the control room is controlled by the magnitude of the current through the loop, which is modulated by the ports of the process subsystem under the control of the controller.
Wireless communications between field devices and controls rooms have begun to replace the traditional two-wire twisted-pair current loops. For example, each field device and/or node associated with a field device is equipped with a wireless transceiver that allows the field device to communicate messages wirelessly via a wireless communication protocol such as WirelessHART (IEC 62591). The plurality of field devices and/or nodes equipped with wireless transceivers create a wireless mesh network that allows a communication between the control room and any field device within range of the wireless mesh network, with messages hopping from node to node across the mesh network to the desired location.
Like other wireless communication protocols, wireless communication protocols such as WirelessHART employed in control system operate in a defined frequency range that is further sub-divided into a plurality of channels. Communication between two devices using WirelessHART (or some other wireless communication protocol) requires agreement as to the channel on which the communication will occur. However, problems can occur when additional wireless communication protocols (such as WiFi) are operational in the same geographic location as the control system wireless communication protocol. For example, a facility using a control system wireless communication protocol such as WirelessHART may also be employing a WiFi type wireless communication protocol to allow employees to exchange data over a wireless local area network (WLAN). Overlap between the frequencies employed by WirelessHART and by WiFi will result in interference, which may result in messages being lost (i.e., sometimes referred to as packet loss).
To avoid interference between competing wireless communication protocols, it is common to identify the channel(s) being utilized by the competing wireless communication protocol such as WiFi, and then program the control system wireless communication protocol (e.g., WirelessHART) to avoid those overlapping channels. However, blacklisting channels available to the control system wireless communication protocol decreases the number of channels that can be used in a channel hopping sequence and therefore decreases the resiliency of the wireless communication system. The term “resiliency” is used to describe the ability of the wireless network to operate despite intentional or unintentional interference on a channel. For example, typical wireless systems employ channel-hopping among a plurality of channels to prevent a malicious user from jamming a particular frequency to disrupt communications. As the number of channels used by a particular wireless system decreases, the resiliency of the system similarly decreases.